In medium bowl, stir together salsa, tomato, scallions, lime juice and cilantro. Set aside.
On large sheetpan, place chicken nuggets. Place in oven and bake 3 minutes. Place tortilla taco shells on separate sheetpan; add to oven. Bake chicken nuggets and taco shells for 4- 5 minutes more, until shells are crisp and chicken and heated throughout.
While chicken and shells are baking, refried beans in medium bowl. Add cayenne pepper and stir to mix well.
To prepare tacos, spread a spoonful of refried beans in each taco shell. Add two nuggets. Pass salsa, cheese and lettuce separately, to be sprinkled on tacos.