Heat oil, in large skillet, over medium–high heat. Add coriander and cook, stirring, for 10 seconds. Add onions, Easy Onion and Ginger; cook, stirring, about 5 minutes. Add garlic, serrano pepper, garam masala, salt, turmeric, and cayenne, and cook, stirring, until fragrant, 30–45 seconds. Add potatoes and cook, stirring for about 3 minutes. Add peas and cook, stirring, for 1 minute. Remove from heat and add cilantro and lemon juice. Stir to combine, adjust seasoning, to taste. Let cool.
Preheat deep fryer oil to 350°F.
Cut each circle in half. Spoon 2 tsp of filling in center of each half–circle. Brush edges with water and fold dough over the filling. Press edges together with a fork to seal. Place on a baking sheet and repeat with remaining ingredients.
Add samosas to hot oil in batches and fry, turning, until golden brown, about 10 minutes. Remove with slotted spoon and drain on paper towels. Combine cilantro and sour cream in a small bowl, season with salt and pepper. Serve with samosas.