Preheat the oven to 450°. In a large bowl, toss the potatoes with the onion, garlic, crushed red pepper and olive oil and season with salt. Spread the potato mixture in a large glass or ceramic baking dish. Add the sun-dried tomatoes and lemon slices to the bowl and toss with any remaining oil from the tomatoes. Scatter the sun-dried tomatoes and lemon slices over the potatoes.
Bake for about 25 minutes, or until the potatoes are tender. Stir in the hearts of palm and roast for 5 minutes longer. Add the sardines and roast for about 1 minute longer, just until heated through. Serve the pan roast right away.