Seed and slice the 2 bell peppers. Slice the onion into half-moons.
Place the chicken breasts in the base of the slow cooker and drizzle the olive oil and vinegar over the top. Sprinkle a little salt and pepper over the top and then add the sliced bell peppers and onions over the top.
Set on low and cook for 8 hours. Once done, shred the chicken loosely with 2 forks and strain off the juice. Spoon the chicken, peppers and onions into the hoagies.
Slice the Provolone cheese and lay on top of the chicken and veggies. If need be, run under the broiler for 1 minute to melt cheese, or add to small toaster oven to melt cheese.
Prepare the salad.
Serve Slow Cooker Chicken Philly Cheesesteak Sandwiches with salad and chips.