Preheat oven to 375°F. While the oven is preheating, mix your fajita seasoning, shell your shrimp and slice your peppers and onions.
Place peppers onion, and shrimp evenly on a a medium sized sheet pan (16x11 or thereabouts). Coat with fajita seasoning, and drizzle with oil; mix well.
Place sheet pan in the oven for 12-15 minutes, until shrimp is opaque and peppers are tender. Serve with tortillas and your favorite sides and enjoy!