Heat oven to 300 degrees. Place buns on top rack and toast for 5-10 minutes, flipping buns halfway. Remove and set aside.
Warm up a large skillet on the stove over high heat. Add avocado oil and allow to come up to temp.
When the oil is hot, add onions, garlic and corn and sauté for a few minutes until onions begin to caramelize, about 3 minutes.
Reduce heat to medium-high and add the tomato paste, spices, vegetable broth and nutritional yeast. Stir well until the mixture thickens, about 2-3 minutes. (Add a splash more vegetable broth if you feel the sauce is too thick.)
Add the lentils and continue stirring gently to mix ingredients for 3-4 minutes more, until lentils are cooked through.
Gently fold in the collard greens and cook until greens are warm. They should be a bright, vibrant green. Remove from heat.
Fill toasted buns with the warm sloppy joe filling. Serve immediately.