Put the oil, garlic, and red pepper flakes in a 10- to 12-inch skillet over medium-low heat. Cook until the garlic is fragrant and starts to sizzle slightly, about 3 minutes. Reduce the heat to low if the garlic starts to brown. Stir in the lemon zest, 1/4 teaspoon salt, and a few grinds of pepper. Raise the heat to medium high and add the broccoli raab, turning to thoroughly coat in the oil and spices. Turn frequently, until it is heated through, 1 to 2 minutes. Turn off the heat, sprinkle lemon juice over the broccoli raab, toss again, and season to taste with salt and pepper.

To blanch, drop trimmed (but uncut) broccoli raab into boiling salted water. After two minutes (even if the water hasn't returned to a boil), drain and refresh under cold water.