SAN DIEGO — A San Diego startup aims to shake up the oatmeal category with high-protein recipes and nostalgic flavors. Founders Nilou Shahryari and Jason Weilenmann launched ONO Overnight Oats during lockdown last year and have since steadily built an online following among fitness and outdoor enthusiasts.

The offerings combine organic gluten-free oats, chia seeds and flax seeds with whey protein or a plant-based protein blend. Flavors include cereal milk, pancakes and syrup, caramel apple, vegan blueberry muffin, vegan peanut butter banana split, vegan rocky road, and vegan mocha chip. Packaged in single-serve packets, the products are prepared with the addition of milk or a dairy-free alternative.

The overnight oats trend emerged several years ago on social media as a convenient, customizable and healthy breakfast preparation. A handful of brands, including Quaker Oats, commercialized just-add-milk varieties, while makers such as Mush and Brekki offer ready-to-eat options for grab-and-go consumption. ONO Overnight Oats contain more protein — 25 grams per serving — and less sugar than similar products in the marketplace, said Ms. Shahryari, who previously held an international marketing and global communication role at Halo Top Creamery.

“What we focus on is to provide a fully balanced meal,” she said. “We love carbs, but we wanted to ensure it’s also high in protein and a good mix of healthy fats as well.”

The products contain lion’s mane mushroom, which is linked to improved cognitive performance, immune health, reduced anxiety and anti-inflammatory properties, according to the company.

ONO Overnight Oats debuted online at in August, and until recently products have been packed in a local commercial kitchen. The founders plan to soon partner with a co-manufacturer and hope to expand into retail locations this year.

“Right now since we’re so new we’re focused on building as much awareness as possible,” Mr. Weilenmann said. “We would love to be in retail, and we would love to get it in gyms and yoga studios and on college campuses.”

The company surveys its online community for suggestions of additional flavors. Future recipe development will focus on transitioning to a cleaner label. Some of the formulations contain artificial flavors and sweeteners to achieve specific taste profiles and macronutrient breakdown, Ms. Shahryari said.

“Our goal is to bring the line to be fully natural, but we found our consumers are more focused on the concept of taste is king,” she said. “If I say this tastes like cereal milk, I want it to taste like cereal milk.”

Mr. Weilenmann added, “As we continue to grow, we are definitely open to discovering other product lines. But now want to focus and make sure we nail this one.”