Preheat oven to 450 degrees.
Toss sweet potatoes and bell peppers, separately, with salt and pepper and olive oil to coat. Spread in single layer on baking sheet and roast until the veggies are browned but still firm (15-20 minutes for sweet potatoes, 10 minutes for bell peppers). Let cool briefly.
Whisk the oil, vinegar and syrup together until smooth and incorporated. Add salt and pepper to taste. Lightly toss the vegetables, onions, parsley and oil and vinegar mixture.
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