Let greens thaw for about 30 minutes.
Cut onions into long, thin slices and fry in olive oil until brown. Crush garlic and cut each crushed clove into 3-4 pieces. Add garlic to the onions and cook 5 minutes on low heat. Add greens. If using frozen greens, cook 45 minutes, covered. If using fresh greens, don’t cover and cook about 30 minutes.
Dice tomatoes and cut jalapenos into long thin strips. Add tomatoes and jalapenos and cook uncovered for 15-20 minutes. Season with salt and pepper to taste