How do you get your 7month to open his mouth to eat meats and veg?

I'm assuming you're still feeding your baby breastmilk or formula?  Yes?  Good.  In that case, don't stress about the meat and veg.  He's getting all the nutrients he needs right now from his milk.  Everything else is gravy - basically, you're teaching him the physics of eating, of putting food in his mouth and having to chew before swallowing.  It's not so much about nutrients as it is about practice.

If he eats the yogurt, cheer and continue feeding yogurt.  After a few weeks, try a new veg or meat, and see if he'll take it.  Taste buds change rapidly at this age - something he doesn't like now, he might decide in another two months is his favorite thing on the planet.  Remember to stick to the 4-day rule on all new foods - that is, don't introduce more than one new food type in a four day span, to ensure that he's not allergic.  (MUCH easier to determine an allergy when you can definitively say what's new!) 

Good luck!  I'm sure he'll be eating both meat and veg like gangbusters in six months' time.  :)