the thing that every expert screams every time they have a chance—AVOID PROCESSED FOOD.

The USDA defines processing as:

washing, cleaning, milling, cutting, chopping, heating, pasteurizing, blanching, cooking, canning, freezing, drying, dehydrating, mixing, or other procedures that alter the food from its natural state. This may include the addition of other ingredients to the food, such as preservatives, flavors, nutrients and other food additives or substances approved for use in food products, such as salt, sugars and fats.

Basically, don’t do… anything?

I think it'd more accurate to avoid ultra-processed food, and not minimally processed. This new concept was created by researchers from the University of Sao Paulo to really clarify this issue, and it defined roughly as "food containing weird ingredients that you'd never have at home". 

https://www.fsp.usp.br/nupens/en/food-classification-nova/

Ultra-processed foods – which can be foods and drinks – are not really foods but formulations of substances obtained by fractionating foods from the first group. These substances include sugar, oils, and fats for domestic use, protein isolates or concentrates, interesterified oils, hydrogenated fat, modified starches, and various substances for exclusive industrial use. 

Added colors, flavors, emulsifiers, thickeners, and other additives that give the formulations sensory properties similar to those found in foods from the first group are added into ultra-processed foods. They also serve to disguise undesired characteristics of the final product. Despite the claims commonly seen on the packaging of ultra-processed products, unprocessed foods are just a small percentage of their composition or are simply absent, as in the case of “strawberry flavored” or “grape flavored” products. 

The processes and ingredients used to manufacture ultra-processed foods are developed to create highly profitable products (low-cost ingredients, long shelf life, branded products) that can replace all other Nova food groups. Their convenience (imperishable, ready-to-eat), hyper-palatability (extremely tasty and flavorful), promotion by transnational corporations, and aggressive marketing give ultra-processed foods huge market advantages over all other food groups. 

Ultra-processed foods include soft drinks, dairy drinks, fruit nectar, powdered mixes for making fruit-flavored drinks, ‘packaged snacks’, sweets and chocolates, cereal bars, ice cream, packaged bread and other bakery products, margarine and other butter substitutes, biscuits, cakes and cake mixes, morning cereals, pies, pasta dishes and pre-prepared pizzas, chicken and fish nuggets, sausages, hamburgers and other reconstituted meat products, instant noodles, powdered mixtures for preparing soups or desserts and many other products.