Preheat the oven to 400 degrees F. Spray a 13 by 9-inch glass baking dish with cooking spray.
Remove the stems from the chard. Course chop the leaves.
In a large nonstick skillet, heat the oil over medium-high heat. Add the onion and cook until soft, about 5 to 7 minutes. Add the garlic and cook for 1 minute longer. Add the chard and cook, stirring constantly, until wilted, about 2 minutes. Allow the mixture to cool slightly.
Place the ricotta cheese, peas, mozzarella cheese, Parmesan cheese, basil, salt, and pepper in the bowl of a food processor. Add the cooled chard mixture and blend until smooth.
Layer lasagna noodles and cheesy chard mixture in your baking dish until both are gone.
For cheese sauce: In a medium saucepan, bring milk and half and half to a simmer, over medium heat. Reduce heat to low. Add the fontina cheese and cook, stirring constantly, until the cheese is melted and the mixture is smooth. Remove the pan from the heat. Sauce will be thin, but will thicken as it bakes and cools. Stir in the Parmesan cheese and basil.
Pour the sauce over lasagna noodles and sprinkle with the mozzarella cheese. Bake for 30 to 35 minutes until the top is golden. Cool for 5 minutes before serving.