Sauté the onions then add the chicken stock and tomatoes and bring to a boil. Add the chilies to rehydrate and simmer, stirring occasionally.
Blend the marinade
Let the sauce cool, then add to a blender and puree until completely smooth. Stir in lemon juice and season the sauce to taste with salt.
Add shrimp to marinade
Add the shrimp to a large mixing bowl and season with salt and pepper. Pour the chili sauce over the top and marinate for about 10 minutes.
Cook the shrimp
Heat a skillet over med-high heat, add remaining oil and heat. Working in batches, remove shrimp from the marinade, and add to the pan. Cook shrimp until pink and no longer translucent, about 1 min per side.
Serve the shrimp diablo
Remove the cooked shrimp to a platter and repeat with the remaining shrimp. Top the cooked shrimp with serrano, green onions and cilantro. Serve immediately.