Rinse about broccoli rabe and discard tough stem ends and yellowed leaves. Halve stems lengthwise if they're more than 3/8 inch thick. Then cut pieces into 3- to 4-inch lengths. Pour olive oil into an 11- to 12-inch frying pan over high heat. Add broccoli rabe, hot chili flakes, and 3 to 4 tablespoons water. Stir-fry until greens are just tender to bite, 5 to 6 minutes. Serve as a vegetable or mix with hot cooked pasta. Season with salt to taste.