Prepare 25 ounces frozen cheese ravioli according to package directions. Drain and set aside.
Chop 1 medium onion.
Thinly slice 2 summer squash.
In a large skillet, heat 2 teaspoons oil and add onion. Cook until onion is tender.
Add squash. Sauté, stirring occasionally, about 5 minutes until squash becomes tender.
Add ½ teaspoon salt and ½ teaspoon pepper.
Melt 1 tablespoon butter.
In a small bowl, combine 1 cup milk, 1 tablespoon flour, and butter; mix until well blended.
Pour milk mixture and 1 teaspoon lemon juice into squash pan and cook over medium heat about 3-5 minutes until slightly thickened.
In a large bowl or in the pan the ravioli was cooked in, mix together the cooked, drained ravioli with the squash mixture. Add ¾ cup grated parmesan cheese and stir until cheese has melted.
Serve warm (garnish with additional cheese if desired).
Notes
Tortellini or gnocchi can be substituted for the ravioli for variety, and you can mix in sliced zucchini for some of the squash for more variety.