Cook spaghetti per package directions. Drain and set aside.
Melt butter in a large skillet until it sizzles. Add onion, shrimp, green pepper, garlic, salt & pepper. Cook over medium heat, stirring occasionally, until shrimp turns pink. Stir in tomatoes and basil.
Place the cooked spaghetti into a large bowl and top with shrimp mixture. Sprinkle with cheese and toss to combine.