Preheat oven to 425°F. In a mixing bowl, toss blood orange slices and scallions with 1/2 tbsp olive oil and salt and pepper to taste. Lay the sliced oranges and scallions evenly on a baking sheet lined with parchment paper, drizzling with any remaining oil from the mixing bowl.
Roast for 10-15 minutes, shaking the pan every five minutes to make sure the oranges don't burn.
Remove from oven and let cool for at least 5 minutes.
While the oranges and scallions are roasting, combine the red onion and lemon juice in a bowl and let sit for 5 minutes, allowing onion to soften.
Toss the salad greens, mint leaves, remaining olive oil and red onions together. Add roasted blood orange slices, scallions and any optional additions, tossing gently to combine. Serve immediately.