Place an oven rack in the center of the oven and preheat to 350 degrees F. Spray a baking sheet with vegetable oil cooking spray and set aside.
In a medium skillet, heat the oil over medium-high heat. Add the pancetta and cook, stirring frequently, until brown and crispy, about 5 to 7 minutes. Using a slotted spoon, remove the pancetta and drain on paper towels. Add the onion to the pan and cook until translucent and soft, about 5 minutes. Set aside to cool for 10 minutes.
In a medium bowl, combine the onion, pancetta, cheeses, and peas. Season with salt and pepper, to taste.
Using a paring knife, cut 1/2-inch from the stem-end of the peppers. Remove the seeds and veins. Using a small dessert spoon, fill each pepper with the ricotta mixture. Place the filled peppers on the prepared baking sheet and bake for 15 to 18 minutes until the peppers begin to soften. Remove from the oven and cool for 10 minutes.
Arrange the peppers on a platter and serve.