Roasted Romaine Hearts - 1 Romaine lettuce heart, Olive oil spray, Salt and pepper - Heat oven to broil on high. Lightly spray a baking sheet with olive oil. Slice Romaine heart down the center lengthwise. Open it up and place on the baking sheet. Spray with olive oil and season lightly with salt and pepper. Broil for 5-8 minutes, depending on how hot your broiler gets. The lettuce should be browned in spots but not burnt. Dress as you wish and enjoy!