Heat up your oil in a skillet (one that has a cover) until shimmering, then add the minced garlic, onion, chili, and ginger. Cook for around 3-5 min, stirring frequently.
Add the spices - turmeric, salt, cumin, coriander, and cayenne (if using). Stir constantly for 2 minutes. If the mixture starts to try out, add a little water (around 1 tbsp).
Add the minced lamb, and cook for around 5 minutes until browned.
Add the diced tomatoes and stir. Turn the heat down (med low to med), then add yogurt tablespoon by tablespoon. As you add each tablespoon, stir to incorporate.
Cover, and simmer for around 15 minutes. Add peas, stir and cook for 1 additional minute.