In general, oats are not considered gluten-free. However, evidence does show that uncontaminated oats are well tolerated by most people with coeliac disease. Please choose your oats carefully if you would like to make this recipe gluten-free.
Traditional quark does not contain rennet - but check the packaging for non-animal rennet. If you cannot find quark, switch 80g of cottage cheese per 100g quark for a similar calorie and protein count.