In a medium bowl, combine the avocados, onion, jalapeno and lime juice; season with salt.
Dust the fish fillets on both sides with the chili powder and season with salt. In a large skillet, heat the olive oil over medium-high heat. Add the fish skin side down and cook until opaque around the edges, about 1 1/2 minutes; turn and cook for 15 seconds more.
Drizzle the cut side of the roll tops with olive oil. Spread the guacamole on the roll bottoms, then top with a layer of radishes and the fish fillets. Set the roll tops into place and serve with the lime wedges.