Combine panko bread crumbs, salt, garlic powder, and black pepper in a bowl. Place buttermilk, flour, and eggs each into 3 separate bowls.

Dip chicken breasts into buttermilk, then dredge with flour. Dip flour-coated breast into egg and press firmly into panko mixture until fully coated on all sides.

Heat vegetable oil in a large skillet over medium-high heat. Place coated chicken breasts into the pan and cook until golden, crispy, and no longer pink in the centers, 2 to 3 minutes per side. Remove from the pan and slice through the middle of a chicken breast to check that it is fully cooked. Set aside on a paper towel-covered plate to absorb excess oil.

Warm 2 tablespoons olive oil in a medium heavy pot over medium heat. Add onion and shallot and saute until both are nearly clear, 5 to 7 minutes. Reduce heat to medium-low. Add tomatoes, basil, garlic, herbes de Provence, red pepper flakes, salt, and black pepper. Cook until tomatoes are softened and water coaxed from them begins to evaporate, about 10 minutes.

Mix chicken broth and white wine into the pot. Bring to a simmer and maintain heat until sauce reduces, 5 to 7 minutes. Blend, using an immersion blender or a regular blender working in batches, until very smooth. Pour half-and-half into blended mixture and slowly add Parmesan cheese, stirring until melted. Use an immersion blender again to smooth sauce, if needed. Let simmer for another 10 minutes; season as needed.

While sauce is simmering, fill a large pot with lightly salted water and bring to a rolling boil. Cook fettuccine at a boil until tender yet firm to the bite, about 8 minutes. Drain; place pasta onto a plate and top with sauce and panko-crusted chicken.