In a large medium heavy pot over medium heat, warm coconut oil. Add collards and broth. Cover and cook until greens wilt, about 3 minutes, stirring occasionally. Uncover and cook until juices slightly thicken, about 4 minutes. Sprinkle with salt and pepper; set aside. Combine avocado with lime juice and cilantro. Warm corn and beans in microwave oven for 1 minute; warm tacos in microwave. When ready to assemble tacos, combine collards, corn, beans, avocado and tomatoes. Fill warmed tacos with vegetable mixture.