Prepare the bacon, reserving bacon grease.
In skillet, add ½ of the reserved bacon grease, 1 cup diced onions, 1 cup minced bell pepper, 2 minced garlic cloves, and tomatoes. Sauté until soft. Remove from heat and put in a blender. Add 3 ounces vinegar. Blend well.
With the blender running, slowly add 4 ounces of oil until well combined.
In a skillet, heat remaining bacon grease and add 1 bag mustard greens. Wilt for 30 seconds. While still in the pan add the blended mixture into the greens. Salt to taste. Note: If using green onions sauté and sprinkle on top.
Serve immediately.