Combine the olive oil, lemon juice, vinegar, garlic, salt, sugar, and crushed pepper flakes in a jar with a lid and shake well to combine.
Slice the roasted red bell peppers into thin strips. Dry the spinach thoroughly and tear into bite-size pieces. In a large salad bowl, combine the roasted red peppers, spinach, zucchini, and scallions.
Before serving, toss with dressing.