Heat oven to 400 degrees F. Heat 1 tablespoon oil in a skillet over med-high heat. Add onion and cook, stirring, until softened. Add beef and cook until browned. Mix in the beans and 1 cup cheddar.
Spread 1 cup enchilada sauce in the bottom of a 9x13 baking dish. Roll up beef mixture in tortillas and place rolls seam-side down in dish. Top with remaining cup of enchilada sauce and cheddar.
Bake until cheddar is brown in spots, 10 to 15 minutes.
Meanwhile, wipe out the skillet and heat the remaining tablespoon of oil over med-high heat. Add zucchini and 1/4 teaspoon salt and cook, tossing occasionally, until tender and golden, 8-10 minutes.
Top the enchiladas with sour cream, salsa, or cilantro based on personal preference. Serve with zucchini.