1. Preheat the oven to 375 degrees.
2. Place the chicken breast between two sheets of plastic wrap and pound with a rolling pin or meat mallet until ¼-inch thick.
3. Remove the top layer of plastic wrap and spread the onions and cheese over the chicken breast in an even layer, leaving about an inch of chicken uncovered at the top (wide end) of the breast. Sprinkle the chicken with pepper.
4. Starting at the pointed end of the breast, roll the chicken tightly, so the cheese mixture is enclosed within the meat in a spiral. Wrap the roulade in the bottom layer of plastic wrap and refrigerate.
5. Place the bread, hazelnuts, thyme, salt, and pepper in a food processor and blend until the mixture is an even powder.
6. Remove the chicken from the refrigerator and unwrap it. Lay out the plastic wrap flat and place the rolled breast at the top edge. Spread the bread mixture evenly beneath the roulade, so it covers the width of the chicken. Carefully roll the chicken over the bread crumbs to coat it evenly.
7. Heat the oil over medium heat in an over-safe skillet large enough to hold the roulade. When the oil is hot, place the chicken in the pan, seam side down. Cook until lightly browned. Then, rotate the roulade until it is evenly browned on all sides. Reposition the roulade, so it is seam side down again. Place the entire pan in the oven for 20 minutes, or until the roulade feels firm. Turn the roulade once during cooking to avoid burning one side.
8. Remove the pan from the oven, place the roulade on a cutting board, and slice it into six rounds.
Serves 2. Recipe can be doubled or tripled.
Note: If you do not have an oven-safe skillet, you can cook the chicken completely on the stove top. Use ¼-cup of olive oil instead of 2 tablespoons to prevent burning and sticking. Simply continue turning the chicken until it feels firm to the touch.