Preheat the oven to 400°F.
Arrange the diced sweet potato on a baking sheet and drizzle it with a tablespoon of olive oil. Use your hands to rub the oil into the sweet potato. Place the baking sheet into the oven and roast the sweet potato for about twenty minutes, until the pieces are easily pierced with a fork.
When the sweet potato has just a few minutes left to go, coat the bottom of a large skillet with the remaining tablespoon of oil and place it over medium-high heat. Give the oil a minute to heat up, then add the onion. Sweat the onion for about five minutes, stirring frequently, until it becomes soft and just begins to brown.
Add the bell pepper to the skillet and cook it with the onion, stirring frequently, for about two minutes, until it starts to become tender and brightens in color.
Add the crumbled tempeh to the skillet. Continue to cook the mixture for about five minutes, stirring occasionally, until the tempeh begins to brown and crisp in spots.
Add the minced garlic, cumin, and smoked paprika. Stir everything well and cook the mixture for about one minute, until the garlic and spices become very fragrant.
Stir in the soy sauce, maple syrup, and lemon juice. Continue cooking the scramble and stirring frequently for another minute or two, just until most of the liquid dries up.
Stir in the sweet potato (Note 1).
Remove the skillet from heat. Season with salt and pepper to taste, and/or some additional soy sauce. Top the scramble with avocado and scallions. Serve alone or in tortillas or toast.