In a large bowl, toss together sweet potatoes, maple syrup and thyme to coat evenly. Spread onto parchment paper lined baking sheet and roast in 220°C (425°F) oven for about 30 minutes or until tender and golden. Return to bowl.
Meanwhile, using a serrated knife, cut both ends off grapefruits. Using sawing motion, cut skin and white pith off and discard. Cut grapefruit between membranes into segments into sweet potato bowl. Stir to combine.
In another bowl, toss spinach with vinegar, oil and pepper. Divide among plates and top with roasted sweet potato and grapefruit mixture.
*Grapefruit and grapefruit juice can interact with certain medications. Speak to your healthcare provider if you have concerns.