Mushroom and Lamb Sweet Potato Bowls

1 tsp. kosher salt, divided, plus more
1 large sweet potato (about 1 lb.), halved lengthwise
½ fennel bulb (about 6 oz.), thinly sliced, plus fronds (for serving; optional)
½ small red onion, thinly sliced
¼ cup apple cider, coconut, or unseasoned rice vinegar
3 Tbsp. extra-virgin olive oil, divided
½ lb. ground lamb (or beef, chicken or tempeh)
1 tsp. ground cumin
½ tsp. ground cinnamon
1 tsp. Aleppo-style pepper, plus more for serving
8 oz. wild mushrooms, sliced into ¼" slices
½ cup plain full-fat yogurt
2 Tbsp. fresh lemon juice
¼ cup mint leaves

Preparation
Fill a large pot with about 1" water; season with a big pinch of salt. Set a steamer basket in pot. Cover pot and bring water to a boil. Add potato, cover, and steam until fork-tender, 20–25 minutes.
Meanwhile, toss sliced fennel, onion, vinegar, and ¼ tsp. salt in a medium bowl. Let sit, tossing occasionally, at least 10 minutes and up to 30.
Heat 2 Tbsp. oil in a large skillet over medium-high. Add lamb, cumin, cinnamon, 1 tsp. pepper, and ½ tsp. salt and press into an even layer. Cook, undisturbed, until well browned on the bottom, about 4 minutes. Break up into pieces with a spatula and continue to cook, stirring occasionally, until browned, 1–2 minutes. Push mixture to one side of skillet and add mushrooms in an even layer; season with salt. Cook, undisturbed, until beginning to brown and soften, 3 minutes, then stir together with lamb mixture. Continue to cook, stirring occasionally, until mushrooms are golden brown, about 2 minutes more.
Whisk yogurt, lemon juice, and remaining 1 Tbsp. oil and ¼ tsp. salt in a small bowl.

Divide potato halves between bowls and mash slightly with a fork. Top with yogurt sauce and mushroom mixture. Lift fennel and onion out of vinegar with your hands and scatter over bowls; discard vinegar. Top with mint, fennel fronds (if using), and pepper.