Toss the shrimp with 1 Tbs. oil, the chili powder, 1/4 tsp. salt, and 1/2 tsp. pepper. In a medium bowl, mash the avocado with the chipotle and adobo sauce, lime juice, and 1/4 tsp. salt.
Heat 1-1/2 Tbs. oil in a large (12-inch) skillet over medium-high heat until shimmering. Add the shrimp and cook, stirring, until they turn pink and become just firm to the touch, about 2 minutes. Transfer to a large plate.
Reduce the heat to medium, and add the remaining 1-1/2 Tbs. oil to the pan. Add the onion, sprinkle with 1/2 tsp. salt, and cook, stirring, until the onion softens and starts to brown, about 6 minutes. Add the garlic and cook, stirring, for 30 seconds. Add the corn and shrimp, and cook, stirring, until they heat through, about 2 minutes.
Let your guests help themselves by spreading the avocado on a warm tortilla and topping the spread with some of the shrimp mixture, a squeeze of lime juice, and a sprinkling of the cilantro.