There are no shrubs that will fill out in one season and it there were, you wouldn't want such a galloping Gertie. Imagine what it would look like after three.

You can fill in empty areas while your shrubs grow with either annuals or perennials.

I think the legginess is indicative of not enough sun and failure to thrive possibly because of competing tree roots. I note the height to where your windows begin and wonder if you should be thinking shrubs at all. I just discovered Little Devil Ninebark that stays small but not sure how hardy it is. I have lysimachia firecracker received at a plant swap that quickly went from single plant to large, spreading clump. It has dark purple leaves. But it would still take about 3 summers to get full. I have a gold leaf spirea that is spreading quickly and doesn't get tall that gets west sun. Check that one out.

I have 2 'Little Devil' ninebark in less sun and I'm happy to say they are doing very well and have filled out quite quickly. Definitely a good choice for colder zones.

Spirea and red twig varigated dogwood have been fast growers for me.

Thanks for the suggestion so far. Will definitely check out Little Devil Ninebark (looks like it's zone 2), lysimachia (love the idea of colorful leaves), and red twig dogwood (I've always loved the red twigs on some shrubs). We have some spirea already so would like something different.

Should have been more clear in my op by stating that I don't want something that matures in a year, just something that fills in nicely. I don't just want a little tiny clump of small bushes within a year, would like something bigger (I suppose that means I just have to buy a more mature plant to begin with).

Appreciate the suggestions!

Hydrangea paniculatas like 'Quickfire', 'Limelight' or 'Little Lamb' will probably be OK there. Depending on the variety, they range in size from about 4' to 8', so choose accordingly. Long blooming (mine start in early July and bloom until hard frost) and don't mind the western sun the way many other types of Hydrangeas do. IME they grow relativley quickly.

I'll second T2D's suggestion of Ninebark 'Little Devil'.

Spirea 'Ogon' has chartreuse/gold foliage, white blossoms, and an arching form that I find more appealing than many spireas.

You can also look into some of the arborvitaes such as Thuja occidentalis 'Bobozam' AKA Mr. Bowling Ball or some of the other relatively small selections which will provide winter interest after leaf fall but before snow.

Another thing that may contribute to failure to thrive may be your mulch scheme. It looks like stone with landscape fabric below. If it is, the landscape fabric won't prevent weeds in the long run (and will actually make weeding more difficult when seeds blow in), and it will prevent adding organic matter to the soil and interfere with water and air movement. Since good soil is the key to healthy plants you may be causing some of your plants' difficulties. IME an organic mulch like shredded bark will help the health of your soil and plants.