On a skillet set over medium heat, coat the bottom with olive oil. Add the onions, serranos and garlic and cook until the veggies have softened, around 5 minutes. Place the shrimp, coriander, salt and pepper in the skillet and cook until the shrimp just turn pink. It's important to not overcook the shrimp. They will continue to cook in the oven as well. No one likes a rubbery overcooked shrimp, so make sure to keep an eye on it.