Preheat the oven to 425°F. Line a small baking sheet with parchment paper.

Combine onion and garlic in a food processor and pulse until finely chopped. Transfer to a large skillet. Combine carrot and celery in the processor and pulse until chopped. Add spinach and pulse a few times more. Add to the skillet. Set the skillet over medium heat and cook, stirring, until vegetables release their liquid. Continue cooking, stirring frequently, until liquid evaporates and vegetables begin to brown, about 8 minutes; add water 1 tablespoon at a time if needed to prevent vegetables from sticking. Transfer to a large bowl and let cool slightly. 

Add chia seeds, ground meat, quinoa, soy sauce and pepper to the bowl and mix gently with your hands. Scrape mixture onto the prepared baking sheet and form into a loaf about 4 inches wide and 10 inches long; dampen your hands if the mixture is very sticky. Spread top of loaf with ketchup. Bake until cooked through and browned, about 40 minutes. Let cool for 5 minutes before slicing.