I give my son eggs,chicken, fish, prawns and whey powder but he around his 20's now
Younger he had yogurt but tofu is also good idea, if he/she likes all the better otherwise it's hiding it in with food

Food Ideas For Picky Autistic Child: The Ultimate Guide -...

Autism Parenting Magazine
https://www.autismparentingmagazine.com
Discover nutritious and sensory-friendly food ideas for picky autistic children

Adding protein to an autism diet involves working with sensory preferences and selective eating behaviors. Practical strategies include blending smooth textures like Greek yogurt or flavorless protein powders into smoothies, mixing nut or seed butters into oatmeal or onto toast, and serving familiar formats like chicken or tofu nuggets.Creative Protein Incorporation StrategiesSneak and Blend: Puree soft beans, lentils, or silken tofu into soups, sauces, or smoothies to boost protein without changing the visual texture.Upgrade Baked Goods: Stir unflavored protein powder, egg whites, or chickpea flour into pancake mixes, waffles, or muffins.Dip and Spread: Pair safe snack foods with high-protein dips like hummus, peanut butter, or blended cottage cheese.Alternative Shapes: Offer fun or familiar shapes using protein-rich ingredients, such as egg cups baked in muffin tins or air-fried tofu cubes.Sensory-Friendly Protein SourcesDairy & Alternatives: Greek yogurt, kefir, and mozzarella string cheese.Plant-Based Options: Smooth nut butters, well-rinsed plain chickpeas, and refried beans.Poultry & Eggs: Scrambled or hard-boiled eggs, finely shredded tender chicken, or turkey lunch meat.Fish: Mild flaky fish like tilapia or soft-cooked salmon pieces

https://jackiesilvernutrition.com/articles/prot...

Nourishing Neurodiversity: Protein for Picky Eaters Guide

https://jackiesilvernutrition.com/articles/protein-for-picky-eaters-guide/

Autism Parenting Magazine – For you and your child

https://www.autismparentingmagazine.com