In a large skillet with high sides, heat the olive oil over medium-high heat. Add in the onions and cook until just translucent and fragrant, about 3 minutes.
Add in the curry paste and stir. Continuing stirring for 1-2 minutes, or until the curry paste becomes fragrant (this helps to reactivate the spices in the curry paste).
Add in the vegetable broth and split peas. Bring to a boil, reduce heat, and simmer for 10-15 minutes, or until the split peas have become tender (but not mushy).
Add in the diced tomatoes and coconut milk. Continue to simmer for an additional 20 minutes, or until the mixture is very thick and the split peas are very tender.
Taste and adjust seasoning—some curry pastes are very salt-heavy, so you might not need to add any seasoning at all.
Serve over hot rice and with a side of warm naan bread.