The DJ's here would probably advise you NOT to do what you want to do.
But if you were to do it, and if I put myself in your shoes, I would:
Find a very nice restaurant (dimly lit, more expensive, but not so expensive that it'd scare your girl). Have a nice meal, try to talk about happy things, drawing from the experience you both have had.
Then walk to a quiet park or something, where it is quiet. Then stop talking for a few moments and let the tension build up. Then ask her.
Alternatively, after the dinner, you can go to your place, where you should have some romantic but light music, with the light dimly lit and all that. Give her some kino and then ask.
It's a very AFC thing to do, but if you want to do it, and want it to be romantic, then let's go all the way.
Warning: this is not a DJ speaking, so you may want to ask for a second opinion.