Tuna- and Potato-Stuffed Ancho Chiles

1. Bring 3 cups water and piloncillo to boil in medium saucepan. Add white vinegar, canela, and salt; simmer until piloncillo has dissolved, stirring often, about 1 minute. Remove from heat. Add chiles and soak until softened, occasionally pressing to submerge, about 1 hour; drain. Pat chiles dry; slit lengthwise and remove seeds.
2. Cook red-skinned potatoes in pot of boiling salted water until skewer easily pierces centers, about 35 minutes. Drain. Cool, peel, and cut potatoes into 1-inch cubes.
3. Prepare barbecue (medium-high heat). Season tuna with salt. Grill until light brown at edges but pink in center, about 3 minutes per side. Cut tuna into 1-inch cubes. Whisk together 1/4 cup oil and next 5 ingredients in large bowl. Fold in potatoes and tuna. Season with salt. Fill chiles with tuna-potato mixture.
4. Whisk remaining 1/4 cup oil, apple cider vinegar, and cilantro in medium bowl. Season with salt. In large bowl, toss greens with 2 tablespoons vinaigrette to coat. Divide salad among plates. Top with chiles and avocado slices; drizzle with some of remaining vinaigrette.

Serves 6.

*Note: Piloncillo is Mexican raw sugar shaped into hard cones. Smaller chunks are sometimes labeled panocha. If neither is available, substitute an equal weight of packed dark brown sugar.