Season the veal shanks with garlic salt and black pepper. You will not use it all, reserve the rest for a later step.
Dredge seasoned shanks in flour. You will have some left over.
Heat olive oil in a Dutch oven over medium-high heat until the oil is shimmering. Add veal shanks and sear on both sides until a nice brown crust is formed. Remove meat and set aside.
To the remaining oil in the pan, add onion, celery, carrots, remaining garlic salt, and remaining black pepper. Stir everything together and cook for 5-6 minutes until onion is translucent.
Add tomato paste and stir to combine. Add in chicken stock and white wine. Stir to combine and bring to a boil. Turn off heat and add meat back to the pan.
Cover the pan and place in the oven. Bake for 2 hours, checking liquid level after 1 1/2 hours. If it looks like the liquid is cooking down too fast, you can add another 1/2 cup or so of chicken stock. The sauce at the end will be thick like stew.
Meanwhile, make the gremolata. Chop fresh parsley and onion into fine pieces. Add lemon zest and chop everything together. Serve on top of osso buco.