In a large bowl, combine the tuna, yogurt, hot sauce, chopped red onion, celery, dill, honey, lemon juice, and chili powder. Mix well. Season with salt and black pepper to taste.
Layer the sourdough bread with sliced cheddar, slices tomatoes, and the tuna mix.
On a heated griddle or panini press, add a little butter or olive oil. Add the sandwich and cook 1-2 minutes on each side, until golden brown and crispy.