Cook rigatoni per package directions. Reserve 3/4 cup pasta water.
Meanwhile, heat olive oil in large, deep skillet on medium. Cook shallot, stirring occasionally, until golden brown, 3 to 4 minutes. Add zucchini and summer squash and salt and pepper and cook, stirring occasionally until squash is very tender but still holds its shape. 10-12 minutes.
Add pasta to skillet and toss with squash and grated pecorino cheese, adding the reserved pasta water 2 tbsp at a time to form a sauce that coats the pasta.
Fold in mint and lemon juice; top with additional cheese and pepper if desired. Serve immediately.