In a shallow bowl combine flour, paprika, chili powder and salt. Coat chicken with flour mixture. Heat oil in a large nonstick pan over medium-high heat and cook chicken on each side until it is fully cooked, about 10 minutes. Remove from pan.
In a small bowl, combine hot sauce and butter. Brush each piece of chicken with hot sauce mixture. Allow chicken to cool slightly.
Preheat a sandwich grill or panini press. Arrange bread slices on a work surface and spread each slice with 1 tablespoon blue cheese dressing. Layer cooked chicken and onions on four slices. Cover chicken with remaining four slices of bread, dressing side down.
Brush top and bottom of bread with olive oil and place panini in grill or press and cover. Cook until bread is toasted, about 3 to 5 minutes. Remove from grill and cut each sandwich in half.
Serve sandwiches and celery sticks with extra blue cheese dressing.