In a large, heavy saucepan, heat vegetable oil over medium-high heat. Add onion; cook until browned, 10 minutes. Add garam masala and turmeric, stir to combine. Stir in 3 cups water; bring to a boil over high heat.
Add rice and salt and return to boiling, stirring briefly. Lower heat, cover pan, and simmer; do not disturb rice until water is absorbed and rice is cooked through, 18 minutes.
Uncover pan, mix in peas and fluff rice with a fork.
Cover, set aside for 5 minutes until peas are heated through. Serve.