Can you mix up/purée a part of my dinner?

[RizzleBizzle]

For example If I have spag Bol, roast chicken with pots and veg or pasta with sauce etc?
Can babies eat tuna? I eat a lot of tuna pasta (lazy)
Is that a done thing? In my head I would prepare my dinner as normal but set aside a no salted etc bit for 6.5 mo DD and blend it up a bit until she can take more lumps and proper foods

Yes, you can definitely do that as long as you don't add salt to your food before you've taken her portion out. With the tuna, make sure you buy it canned in spring water or oil; canned in brine is too salty. You also don't need to puree/blend/mash it if you don't want to. Giving it in the same form as you have it is fine from 6 months.

Have you looked at baby led weaning? The idea is basically to give them whatever you had and let them feed themselves with their hands. We just started with ds who will be 6 months on Tuesday. He likes tuna