Some ways that I use to get the cheese all gooey (for salads) is to toss it (the cheese) in with the sautéing ingredients just before serving. For example, if I am sautéing peppers and sliced meat, I'll toss the cheese in there at the last minute or so and stir until I get the gooey consistency that I love. then I pour it over the more delicate lettuce greens. You can also do this alone in a nonstick skillet. Again that depends on the cheese you're melting. This tactic works well with hard, grated cheeses.
If you are working to melt a Camembert or other soft cheese you can microwave them or bake them in the oven and then transfer to them to the salad afterwards. Anywhere from several minutes in the microwave to 10-15 in the oven works well. Keep an eye on the cheese; a whole Camembert while swell up with the heat. when it does, it's hot and gooey and ready to be served.
There is also the tactic of slicing the cheese (if it is of the soft or semi-soft variety) and placing them on slices of toast and broiling them. If you slide the whole salad under the broiler, the salad will melt, but by using the bread or toast slices, you can cook the cheese to your liking without sacrificing the crispness of the salad. Best candidates for this method are goat cheeses, bleus or even individual Bries or Camemberts. (Sliced Camembert will run absolutely everywhere so be watch out!)
I have a Tupperware pitcher that is quite new and when I melt things in it in the microwave, the items don't stick much. Hard cheeses work well in this type of container. Melt cheese here and pour over salad. A really good nonstick saucepan works well too.
I use the saucepan when melting cheese like bleu or Roquefort. If they are really strong, I'll add some crème fraîche or crème fluide (sour cream, single cream...) to mellow out the intense flavor; whisk well together and pour over salad.
If any other readers have some ideas about melting cheeses for salads, please feel free to share them here with the rest of us.