Whisk together olive oil, balsamic vinegar, Dijon mustard, Italian seasoning, minced garlic, salt and pepper for the chicken marinade.
Add the raw chicken to a large ziploc bag, then pour the marinade over, close the bag, letting as much air out as possible. Massage the chicken thru the bag with your hand to make sure it's all well-coated. Place in fridge and let marinade 30 minutes to 3 hours.
Cook tortellini al dente, per package instructions. Then drain them, run them under cold water for 30 seconds, drizzle a little olive oil (so they don't stick), toss them gently, place aside to cool completely, stirring them from time to time.
Put together the salad dressing by whisking olive oil, balsamic vinegar, Dijon mustard, minced garlic, finely chopped shallot, salt and pepper.
Heat up a grill pan, spray with cooking oil. Take out chicken from back with tongs, shaking off the excess marinade. Grill on medium high heat for 5-6 minutes, then flip and grill for another 5-6 minutes (cooking time will vary depending on the thickness of the chicken cutlets). Dispose of the leftover marinade.
Once cooked, place chicken on a plate and let rest for 10 minutes. Then chop into bite size.
Toss together the tortellini, tomatoes, mozzarella pearls, chicken, arugula, basil and most of the dressing and toss gently until all coated.
Add the chopped avocado, adjust salt and pepper, and toss gently. Add more dressing if needed. Serve and enjoy!