HEAT OVEN TO 325ºF.
RESERVE 2 TBSP. EACH ONIONS AND TOMATOES. COOK BACON IN LARGE SKILLET UNTIL CRISP. REMOVE BACON FROM SKILLET, RESERVING 1 TBSP. DRIPPINGS IN SKILLET. DRAIN BACON ON PAPER TOWELS. ADD MUSHROOMS TO RESERVED DRIPPINGS; COOK AND STIR 2 MIN. OR UNTIL TENDER. REMOVE FROM HEAT. CRUMBLE BACON. ADD TO SKILLET WITH REMAINING ONIONS AND TOMATOES; MIX WELL.
BEAT EGGS AND SOUR CREAM WITH WHISK UNTIL WELL BLENDED. POUR INTO GREASED 13×9-INCH BAKING DISH; TOP WITH BACON MIXTURE AND CHEESES.
BAKE 30 MIN. OR UNTIL CENTER IS SET. TOP WITH RESERVED ONIONS AND TOMATOES. LET STAND 5 MIN. BEFORE CUTTING TO SERVE.
