Warm Thai Beef Salad

12 ounces of beef flank steak
1/4 cup of plum sauce
2 tablespoons of red wine vinegar
1 tablespoon of water
1 to 2 teaspoons of hot bean paste
1/4 to 1/2 teaspoon of crushed red pepper
4 cups of torn mixed greens, such as curly endive, spinach, arugula, radicchio, watercress, and or leaf lettuce
One 11 ounce can of mandarin oranges, drained
2 tablespoons of cooking oil
1 red sweet red pepper, cut into strips
1 yellow sweet pepper, cut into strips
3 Serrano chili peppers, seeded and finely chopped
1 clove garlic, minced