Thoroughly rinse turnip greens in cold water about 2-3 times. Remove large, tough veins and slice greens.
Bring a large pot of water to boil. Add greens and cook for 7-10 minutes until just tender.
Transfer into an ice bath. Once cool to touch, strain with a colander, and squeeze out as much water as you can. This yields about 3 cups of cooked greens. Set aside.
Add onions and diced tomatoes into a large skillet or fry pan. Bring to a gentle simmer over medium heat. Toss in peppers, with the stalk still attached. Cook, stirring occasionally until tomatoes are reduced into a chunky sauce. About 10 minutes.
Add in canola oil and fry for 3-5 minutes. Remove peppers and set aside. Season to taste (or slightly over) with salt.
Stir in greens and cook for another 4-5 minutes or until desired tenderness of greens. Adjust seasoning if necessary.
Serve with whole peppers.