Wash and trim sweet potatoes, leaving peel on. Cut each down the middle lengthwise and rub all over with 1 Tbsp olive oil. Place on baking sheet, cut side up, and sprinkle with 1/4 tsp salt, 1/4 tsp pepper, thyme leaves, and chopped sage. Bake in preheated oven for 50 minutes, turning them to face down halfway through cooking time.
Meanwhile, drain and rinse beans and set 1/2 cup aside to dry in single layer on kitchen towel-lined plate. In small saucepan, place remaining beans with bay leaf, thyme sprig, and sage leaves and add enough cold water to just cover. Heat on medium-low for about 10 to 15 minutes, until warmed through. Time the start so they are ready just as sweet potatoes are finishing in the oven, and keep warm in the hot water, adding 1/4 tsp salt. Pat reserved beans with kitchen towel and season with spicy paprika and garlic powder.
Remove sweet potatoes from oven, remove their skins, and place flesh in large bowl. Toss reserved beans on the same baking sheet, coating them in the remaining oil and herbs. Return baking sheet to oven and bake beans for 15 minutes, until crispy, stirring occasionally.
Brush each tortilla on both sides with 1 tsp olive oil and bake on baking sheets for 5 minutes, or until brown, turning halfway through.
While tortillas are warming, with fork, mash sweet potatoes and cover to keep warm. Drain simmering beans.
To assemble tostadas, divide mashed sweet potato among tortillas, add a few simmered beans, and top with spicy crispy beans. Season with 1/4 tsp salt and 1/4 tsp pepper.
Recipe Notes
Per serving: 373 calories; 12 g protein; 8 g total fat (1 g sat. fat); 66 g total carbohydrates (2 g sugars, 16 g fiber); 248 mg sodium