Preheat oven to 350°. Combine panko and sesame seeds on a large baking sheet and bake, tossing halfway through, until panko is dark golden brown and sesame seeds are golden, about 10 minutes. Meanwhile, heat 1/2 Tbsp. oil in a small skillet over medium heat. Add garlic and cook, stirring constantly, until fragrant and golden brown, 1 to 2 minutes.
Transfer panko and sesame seeds to a medium bowl, add chili powder, 1/2 tsp. salt, and garlic (with its oil) and toss well; set aside.
Put half of spinach in a large microwave-safe bowl (glass or ceramic is best). Cook in the microwave on high until warmed through but not yet wilted, 45 to 60 seconds. Add 1/2 Tbsp. oil, 1 tsp. lemon juice, and 1/2 tsp. salt and toss well. Return to microwave and cook, tossing every 30 seconds, until almost completely wilted but not yet giving off liquid, about 1½ minutes more. Transfer to a warm serving bowl and set aside. Repeat process with remaining 1/2 pound spinach, 1/2 Tbsp. oil, 1 tsp. lemon juice, and 1/2 tsp. salt.
Combine both batches of spinach, top with reserved sesame-garlic crumbs, and serve immediately.