Heat oil in a large nonstick skillet over medium-high heat. Add cauliflower and cook, stirring occasionally, until beginning to brown, 4 to 6 minutes. Add scallions and garlic; cook, stirring, until fragrant, about 15 seconds. Add edamame; cook, stirring often, until heated through, 2 to 3 minutes. Whisk the reserved sauce and add it to the pan; cook, stirring, until thick and coating the cauliflower, about 1 minute. Serve sprinkled with crushed red pepper, if desired.