Bring a medium saucepan of salted water to a boil. Add the sweet potato cubes and parboil for 4 to 5 minutes until just fork-tender at the edges but still firm in the center. Drain well and pat dry.
In a mixing bowl, toss the tempeh cubes with the tamari, half the smoked paprika, cumin, garlic powder, and cayenne. Let it sit for 10 minutes while you dice the vegetables.
Heat 2 tbsp olive oil in a 12-inch cast iron skillet over medium-high heat. Add the tempeh in a single layer and cook 4 to 5 minutes per side, without moving it much, until deep golden and crisp at the edges. Transfer to a plate.
Add the remaining 1 tbsp olive oil to the same skillet. Add the parboiled sweet potatoes in a single layer and cook undisturbed for 4 minutes until browned on one side.
Add the onion, bell pepper, remaining smoked paprika, salt, and black pepper. Cook, stirring occasionally, for 6 to 8 minutes until the sweet potatoes are tender and the vegetables have softened with charred spots.
Add the minced garlic and cook for 1 minute, stirring, until fragrant.
Return the tempeh to the skillet and toss everything together. Cook for 2 more minutes to heat through and let the flavors meld.
Taste and adjust salt as needed, then remove from the heat.
Top with chopped cilantro and serve with lime wedges and avocado slices on the side.