Heat 2 tablespoons of olive oil in a large non-stick frying pan over medium-high heat. Slice the chili (deseed it if you prefer less heat), peel and finely chop 2 cloves of garlic, then chop the basil stalks, reserving the leaves for later. Add these ingredients to the pan and stir in the frozen peppers. Peel and finely slice the onion, then add it to the pan. Season with a pinch of sea salt and black pepper. Cook for about 10 minutes, stirring occasionally, until the vegetables are softened and fragrant.