Preheat the oven to 375°F.
Place flank steak and chicken thighs on a large sheet pan.
Slice the bell peppers and red onion into very thin strips. Place on the sheet pan and drizzle everything with the olive oil.
In a small bowl, combine the chili powder, cumin, paprika, brown sugar, oregano, onion powder, and kosher salt. Sprinkle evenly over the meat, peppers, and onion, flipping the meat so that it gets seasoned on both sides.
Place the sheet pan in the oven and bake for 15–20 minutes, or until the flank steak is done to your liking. I baked it for 17 minutes for medium. Remove the flank steak, place on a cutting board, and cover with foil. Place the sheet pan back into the oven for 10–15 more minutes (total cooking time should be 30 minutes), or until the chicken thighs are cooked through and the peppers are tender.
Slice the chicken thighs and flank steak. Serve with pico de gallo and tortillas.