Heat a medium skillet over medium heat. Add the oil and, when warm, add the onion and green onion with a pinch of salt. Cook, stirring often, until soft and translucent, about 5 minutes. Add the jalapeno and chili powder and cook, stirring, 1 minute more. Stir in shrimp with a pinch each of salt and pepper and cook, stirring, just until shrimp are opaque, 1-2 minutes more. Transfer mixture to a bowl and cool.

To the cooled shrimp mixture, add the cream cheese, 1/2 cup of the Monterrey jack, crab, corn and red pepper. Stir very gently to combine, taste and season as needed with additional salt and pepper.

Preheat oven to 350 degrees.

Lay the tortillas on a work surface and divide filling into the centers of each. Roll up and place, seam side down, into a lightly greased 9x13 inch baking dish. Combine the enchilada sauce with the sour cream and spread the mixture over the enchiladas. Top with the remaining 1/4 cup of Monterrey jack and bake until heated through, about 20 minutes. Turn oven to broil and cool 1-2 minutes more, just until tops are lightly browned.

Enchiladas can be filled and placed in the pan (without the sauce), covered and refrigerated up to one day. Just before baking, top with sauce and cheese.