PREHEAT oven to 400ºF. Gently wash beets; pierce in several places with fork. Place beets and onions in center of large sheet of heavy-duty foil. Drizzle with 2 Tbsp. of the dressing. Bring up foil sides. Double fold top and both ends to seal packet, leaving room for heat circulation inside. Place on 15x10x1-inch baking pan. Bake 45 min. or until beets are tender. Remove packet from oven. Let stand 5 min. Cut slit in foil to release steam before opening. Let beets stand in foil until cooled. To peel, gently rub skins with cloth or paper towel until skins are removed. Cut beets into wedges; set aside.
MEANWHILE combine remaining dressing, jalapeno pepper, 1/4 cup of the peanuts and lime juice in blender; cover. Blend until smooth; set aside.
ARRANGE jicama on serving platter; top with beet and onion mixture. Drizzle with dressing mixture. Sprinkle with cilantro and remaining chopped peanuts. Garnish with lime wedges.