Cook sausage in a large skillet over medium heat until no longer pink inside; transfer to a cutting board. Cut sausage into ¼-inch slices; return sausage to the skillet and continue cooking until browned.
Stir in zucchini, yellow squash, and onion; cook for 2 minutes. Add tomatoes with liquid, reduce heat, cover, and simmer for 10 to 15 minutes.
