Preheat the oven to 400ºF/200ºC. Grab two half sheet baking pans - no parchment paper needed.
Roast veggies. Add the sweet potato cubes to one side of the baking sheet. Toss with olive oil, kosher salt, and black pepper then spread into an even layer over 2/3 of the baking sheet. On the other 1/3 toss the sliced cabbage with olive oil, salt, and pepper. Spread out as much as you can, but it's fine if it's overlapping because it'll lose volume at it cooks. Roast for 30-35 minutes, stirring both halfway through.
Add bell peppers. On one half of the second baking sheet, toss the chopped peppers with olive oil, salt, and pepper and spread them into an even layer.
Prepare salmon. In a medium bowl, toss the salmon cubes with olive oil, brown sugar, smoked paprika, onion powder, garlic powder, kosher salt, and black pepper. Add them on the other half of the bell pepper pan with a little space in between the salmon pieces. Cook the bell peppers and salmon for 8-10 minutes (check salmon after 8* see notes below about wild salmon). The salmon should be moist and flake easily with a fork.
Assemble bowls. Layer each bowl with roasted sweet potato, cabbage, bell peppers, mixed greens, cooked salmon, and avocado slices. Add a generous drizzle of sauce over the top. Enjoy!