In a small bowl, mix together yogurt, mint, lemon juice, cumin, cayenne pepper, salt, and pepper. Set aside.
In a large saucepan of boiling water, cook the peas until tender, about 3 minutes. Drain.
In the same saucepan, heat the 1 1/2 tablespoons olive oil. Add the green onions, cover and cook over medium-low heat, stirring occasionally until softened, about 5 minutes. Stir in the peas and a pinch of salt, cover and cook until heated through, about 1 minute. Stir in the butter until melted, then mash with a potato masher and keep warm.
Preheat oven to 350 degrees. Heat medium nonstick ovenproof skillet over medium-high heat. Add the remaining 2 tablespoons olive oil. Use paper towels to pat the salmon dry, then lightly season it with salt and pepper. When the oil is hot and moves easily around the pan, add the salmon skin side down. Sear until the skin is light brown and crispy, about 5 minutes. Turn the fillet over and continue to sear for about 1 minute. Transfer to oven and cook until knife is warm to the touch when inserted into the middle of the salmon, about 5-7 minutes depending on the thickness of the fillet. Let rest for a couple of minutes.
Serve the salmon over the mashed peas and top with a healthy dollop of the spicy mint raita. Garnish with a mint leaf or green onion, if desired.