Preheat the oven to 400 degrees F.
Place the tomatillos, garlic and onion on a baking sheet. Drizzle the vegetables with the olive oil. Season with salt and pepper. Roast the vegetables in the oven until browned and softened, about 15 to 20 minutes. Remove the vegetables from the oven and place the tomatillos and onion in a food processor. Squeeze the garlic cloves out of their peels into the food processor. Add the jalapeno, juice of 1 lemon and lime to the vegetables. Pulse until the mixture is fully incorporated but not pureed. Season the salsa with salt and pepper, to taste, and set aside.