Heat a heavy-bottomed pan over medium heat and add the oil, letting it shimmer.
Add the finely diced onion and sauté for about 5 minutes, stirring often, until it turns golden and fragrant.
Stir in the minced garlic and grated ginger, cooking for another minute until they release a fragrant aroma.
Add the ground turmeric and cumin, stirring briefly to toast the spices for about 30 seconds until fragrant, being careful not to burn them.
Pour in the coconut milk and stir to combine, then season with salt to taste. Bring the mixture to a gentle simmer.
Add the green peas to the pan, stirring well to coat them with the spiced coconut sauce. Cook for 3-4 minutes until peas are tender and vibrant green.
Reduce the heat to low, cover the pan, and let the curry simmer gently for 7-10 minutes, stirring occasionally to meld flavors and thicken the sauce slightly.
Sprinkle the garam masala over the curry and stir in the final squeeze of lemon juice to brighten the flavors. Give it a taste and adjust salt if needed.
Remove the pan from heat and let the curry rest for a couple of minutes, allowing flavors to deepen.
Serve the green pea curry hot, garnished with fresh herbs if desired, alongside rice or crusty bread for a complete meal.