Preheat oven to 350°F.
Mash avocados with lime juice, salt, sour cream, garlic and cumin. Add tomatoes, onions, jalapeño and cilantro, and stir. Fold in chicken to coat; taste to adjust seasoning.
Arrange tacos on a baking sheet and sprinkle some cheese in each. Bake 3-5 minutes to warm, toast and melt cheese. Remove from oven.
Fill tacos with lettuce and chicken salad; top with radishes and pickled jalapeños.