Pour the oil in a large skillet or sauté pan and bring over medium-high heat. Add the onions and cook for 3-4 minutes until softened and golden. Add the ground beef, salt & pepper and cook, breaking up the beef with a wooden spoon until brown and cooked through. Add the garlic, tomatoes, ginger, Garam Masala, and chilies and stir to combine. Cook, stirring regularly, for 3-5 minutes until tomatoes are softened and flavors are combined. Add the peas and reduce the heat to medium. Cook for an additional 6-8 minutes until the peas are softened without being mushy. Stir in the lemon juice and remove from heat. Add more salt to taste if necessary.