Breakfast may be touted as the most important meal of the day, but what's for lunch can make or break a good diet. Whether you're packing up a lunch for work, preparing something at home, eating out or taking a noon meeting, it pays to plan ahead.

Atlanta's Marisa Moore, registered dietitian nutritionist (RDN) in private practice, knows the struggle as well as any of us, and in helping her clients build a lifestyle around healthy eating, she does so herself, too.

"I work from home more often than not," she said. "Still, I plan my lunches. Some of my go-to lunches include a vegetable omelet and a side of fresh grapes for a heart healthy and nutritious sweet treat, [or a] chickpea and spinach salad with tomatoes, garlic, feta and extra virgin olive oil."

Fitness fans on the go don't have to stay at home to keep their diets in line, though.

"If I'm out, I go for bowls. I love a grain bowl with brown rice or quinoa, beans, salad greens and any vegetables available. Finding a healthy lunch while out is easy." Moore cited local spots like like Gusto and MetroFresh as great go-to lunch picks, noting that "eating healthfully is easy and affordable."

Try packing lunches for a daily treat that's as kind to your wallet as your waistline.

"You don't have to pack a boring lunch," Moore said. "Add color, texture and nutrition by tossing in red, green or black grapes into whole grain salads. Use carrots to add variety, crunch and beta-carotene to green salads. Add orange, green or red mini bell peppers to your lunch box for crunch, flavor and loads of vitamin C. These all hold up well in transition."

Whether it's packed from home, bought at the store or eaten on the go, healthy lunches should all share some of the same qualities.

"A well-rounded, satisfying lunch includes a good source of protein: think beans or tofu, fish, boiled eggs, chicken, lean meat," said Moore. She also stressed the importance of whole grains and veggies. "At least half the plate or bowl should be vegetables, or [a combination of] fruit and vegetables. Think spinach, kale, peppers, onions and more."

While many of these ingredients are low in calorie, they add many vital benefits to balanced menu. The biggest benefit? They'll keep eaters full for longer.

"These high-fiber, high-water vegetables will nourish the body and help you feel full when combined with the other elements of the meal," Moore said. That's big—some of the biggest mistakes of would-be healthy eaters revolve around eating too little for lunch and paying for it later. Moore cautions against juice-happy eaters looking to "drink their lunch."

"Opting for a juice or smoothie at lunch can leave you wanting more," said Moore. '"These beverages tend to lack the satiety factor. Some are loaded with sugar which may lead to the dreaded energy crash around 3 p.m."