First, it’s essential that you gain the dude’s trust. Cook him a steak, exactly the way he likes it, and serve the exact type of potatoes he likes, even if that’s french fries.
The next time you make this meal, serve a potato salad. Make it traditional with, you know, parsley or pickles. Mayonnaise if he’s into that.
The next time you cook for him, serve potato salad, but thin out the dressing with more rice vinegar, skip the pickles, and serve it with a cooked vegetable, like eggplant, beets, or carrots. Be sure to throw in something he likes like bacon or croutons.
The next potato salad should have some kind of greens, cooked or raw, depending on what he can handle and some fun raw vegetable, like cherry tomatoes. Dressing, by now, should be something healthy like a honey mustard, home made ranch, or balsamic vinaigrette.
The next potato salad should introduce the dude to the leaf. Make sure your fresh greens are REALLY high quality. This is not the time to be stingy. Think spring mix from the gourmet section of the produce section. Include fun stuff like roasted yellow pepper slices or raisins or both.
Him: What’s that?
You: Potato salad!