It takes a minimum of 10 minutes to do a good job explaining FODMAPs to someone who has never heard of it before...you're just not going to do justice to the topic in 30 seconds with your restaurant server, no matter how hard you practice beforehand. Here are some tips for dining out that might help you get the sort of meal you are looking for:
It helps to be a regular. Start with those restaurants you visit most often.
You might also have good luck with national chain restaurants; such restaurants have professional menu developers and documentation available for ingredients/allergens in each menu item.
For a thorough discussion about your special dietary needs, make an appointment, or at least call the day before around 4 pm, the slowest time of the day in most restaurants.
Many restaurants are trying to cater to diners on gluten-free diets. That is a good place to start, since a gluten-free diet automatically excludes fructan-containing grains. If you have to explain what you need in a real hurry, say “gluten-free, with no onions, garlic, sauce, or gravy.” (You and I know that gluten isn't a FODMAP but there is no need to try to explain all that to the restaurant staff, so save your breath).
You can then go on to review the major ingredients and available substitutions for each meal. Choose simply prepared mains without sauces, since they often contain FODMAPs. Grilled steak, shrimp, or chicken is often available. Grilled or broiled fish and seafood (hold the crumbs) works well, too. FODMAP-friendly side dishes include tossed salad (hold the onions) with oil and vinegar, baked potato, french fries or plain rice (not pilaf), and simply prepared vegetables. Skip the soup, which usually contains FODMAPs. At breakfast, skip the giant donut and go for eggs and bacon with a side of potatoes. Or better yet, a small bowl of oatmeal with a fruit cup. Fruit cups often consist primarily of low FODMAP berries and melon.
When mealtime arrives, relax, and enjoy your meal. Your food for an occasional restaurant meal does not have to be 100% perfect for this diet, as it would have to be for a food allergy or celiac disease. Be sure to thank your server, the cooks, and the restaurant manager for their help, and don't forget to tell your friends or give them a good review!