Combine the chopped pineapple, mango, scallions and cilantro. Add a hefty pinch of salt and the juice from half a lime. Mix well until combined. Taste and adjust seasoning as needed.
Make the fish
Combine the flour, salt, pepper, garlic powder and paprika. Whisk in the egg and add the beer. Whisk until just combined.
Cube the fish into 2 to 3 inch pieces. Pat dry.
Add a few inches of oil to a medium pan. Place over medium high heat until it reaches 375 degrees. Dip a piece of fish in the batter and gently place in the oil. Repeat with half the fish. Flip once golden brown on one side, about 2 minutes. Fry for another 1 to 2 minutes. Let drain on paper towel and finish with flaky salt. Repeat with the remaining fish.
Make the crema
Combine the sour cream, mayonnaise and lime juice in a bowl or squeeze bottle.
Assemble
Place a piece of fish in a corn tortilla. Top with the salsa, crema, a few slices of radishes, a few cilantro leaves, some avocado and a squeeze of lime. Repeat with all tortillas.