1.) Pre-heat the oven to 375ºF. Line a large baking sheet with parchment paper.
2.) Slice the sweet potatoes lengthwise into ½-inch-thick slices. Lay the slices flat on the prepared baking sheet and bake for 35 to 40 minutes, until the edges are browned and the slices are easily pierced with a fork.
3.) While the sweet potatoes are baking, combine the diced tomatoes, red onion, garlic, basil, lemon juice, salt, and pepper in a medium bowl. Cover and let sit until the sweet potatoes are done.
4.) When the sweet potatoes are just about ready, chop the avocado and gently fold it into the tomato mixture.
5.) Top the sweet potato slices with sliced cucumber and baby arugula, and then spoon with 2 to 3 tablespoons of the avocado mixture on top.