In small bowl, mix ricotta cheese and pesto. Stir in mozzarella and Parmesan cheeses.
Spray 4-quart slow cooker with cooking spray. Spread 1 cup of the pasta sauce in slow cooker. Layer with half of the ravioli, half of the ricotta mixture and 1 cup of the fontina cheese. Top with 1 cup pasta sauce and remaining ravioli and ricotta mixture. Pour remaining pasta sauce over top.
Cover; cook on Low heat setting 3 hours.
Sprinkle remaining 1 cup fontina cheese over ravioli. Cover; cook 30 minutes longer or until ravioli is tender. Garnish individual servings with basil.