Arrange tomatoes on piece of wax paper; salt and pepper both sides, using 1 teaspoon of the salt and the pepper.
Combine flour, baking powder, baking soda and remaining 1 teaspoon salt in medium-size bowl. Remove 1/2 cup of the mixture to a piece of wax paper.
Dip both sides of tomatoes in the 1/2 cup of flour mixture. Stir beer and lemon juice into remaining flour mixture. (Mixture will foam.) Stir until the consistency of pancake batter.
Heat oil in large skillet. Dip tomatoes into batter and saute half at a time in hot oil until golden, about 3 minutes on each side. Keep warm in oven while sauteeing remaining tomatoes. Serve immediately.