If you can’t find “Italian seasoning” at your grocery store in the spice aisle (or if you don’t want to buy it), it’s just basically a mix of basil, rosemary, thyme, and oregano, so you can just mix those together at home and use 2 teaspoons of the mix!
If you don’t have an immersion blender, you can puree this with a regular blender in batches. Just add some of the 1/4 cup of olive oil to each batch as you blend it so it’s emulsified throughout the whole sauce.
I portion this into several tupperwares, put one in the fridge, and put the rest in the freezer. When my fridge sauce is running low, I’ll pop a tupperware out of the freezer and let it thaw!