Heat a large Dutch oven over medium-high heat. Add the bacon and cook until crisp, about 5 minutes. Add the garlic, shallots, ginger, and red pepper flakes. Cook, stirring occasionally, until caramelized, about 3 minutes. Pour in the broth, milk, and soy sauce, then whisk in the miso and chili paste. Reduce the heat to medium-low and simmer 10 minutes.Meanwhile, make the Katsu. Place the Panko and sesame seeds in a shallow bowl. Season with salt. Dredge both sides of the chicken through the Panko, pressing to adhere by using your fist to really pound the crumbs in. Place the chicken on a plate.Heat a few tablespoons of oil in a large skillet over medium-high. Add the chicken and cook until golden brown, 3-4 minutes. Flip the chicken and cook until golden brown on the other side, about 3-4 minutes. Transfer to a cutting board and season with salt. Slice into thin strips.To the soup, stir in the noodles, spinach, and sesame oil. Let sit 5 minutes or until the noodles are soft. To serve, divide the noodles between bowls and ladle over the soup back overtop. Add the chicken. Top as desired with eggs, green onions, sesame seeds, and chili oil. Serve immediately.