Store-bought Massaman curry paste is used to marinate lean flank steak and create a rich pan sauce in this five-ingredient dinner.
Season steak with salt and pepper. Brush with 1 tablespoon curry paste; let stand 10 minutes. Combine rice, 1 3/4 cups water, 1 tablespoon oil, and 3/4 teaspoon salt in a saucepan. Bring to a boil, then stir once, cover, and reduce heat to low. Simmer until rice is tender, about 15 minutes. Add white and light-green scallions; cover to steam.
Heat a large cast-iron skillet over medium-high. Swirl in 1 tablespoon oil. Add steak; cook, flipping once, 7 to 9 minutes for medium-rare. Transfer to a carving board. Reduce heat to medium. Add 1 tablespoon oil and remaining 2 tablespoons curry paste to skillet; cook 1 minute. Add 3/4 cup water; cook until reduced to 1/2 cup, 30 seconds. Transfer to a bowl; cover. Wipe skillet clean; add remaining 1 tablespoon oil and heat over medium. Add snap peas, season with salt, and cook, stirring occasionally, until crisp-tender, 2 to 3 minutes. Fluff rice; stir in scallion tops. Slice steak against the grain; serve with rice, peas, and curry sauce.