Preheat oven to 425. Combine flour, cornmeal, baking powder, salt, and buttermilk powder in a medium bowl. Add olive oil. Stir well to combine.
Add chicken tenders and 1/2 cup of the flour mixture to a large zip top plastic bag. Seal and shake to coat chicken with flour mixture.
Divide chicken evenly among 6 individual au gratin dishes, or to the bottom of a 13X9 baking dish. Bake, uncovered, at 425 for 12-14 minutes, turning once, or until browned and cooked through.
While chicken is baking, add both kinds of beans, tomatoes, salsa, and ketchup to a medium saucepan. Bring to a boil, stirring occasionally. Remove from heat and set aside.
Stir remaining flour mixture with milk, butter, and green onions. Stir until soft dough forms. Set aside.
When chicken is done, remove dishes from oven. Remove chicken and keep warm. Pour bean mixture into dish(es). Spoon dough onto warm bean mixture by the spoonful. Tuck chicken around the dish(es) so that one end is sticking into the bean mixture and the other end is sticking out.
Return to oven. Bake uncovered 20-25 minutes. Top with sour cream, cheese, and green onions, if desired.