Cover that garden in a tarp and starve the dandelions and grass to death. Then till in their plant bodies as fertilizer to conquer your garden!
Love the raised planter beds. My wife was doing them back when we were in the south and I don't think she'll ever have a traditional garden again. Her knees don't like all the bending, so being able to pull up a chair beside a planter and do the weeding without being on her hands and knees was great.
Apparently beneath all the grass and dandelions lies a horrible soil full of clay and rocks... I'm not looking forward to meeting them! xD
My knees aren't really a fan of bending either and thanks to your comment I just realised that I need more raised planters, haha. Sitting on a chair while doing all the things sounds amazing and my knees are now screaming in advance at my future garden bed.