Melt butter in a large dutch oven over medium heat. Add onions and saute until golden. Season with salt and pepper.
Add gluten-free pasta, bone broth, water and bring to a boil.
Reduce heat to medium-high and cook, stirring frequently until al dente (depending on brand and content of gluten free pasta). This is usually no more than 6 minutes.
Take off heat, stir in chard, parmesan, lemon zest and lemon juice and stir to combine.
Fold in flaked canned tuna. Serve immediately with a drizzle of extra virgin olive oil and freshly grated parmesan cheese.
The information shown above is an estimate provided for your convenience by an online calculator. It should not be considered as a substitute for a professional nutritionist's advice. Please see our complete Nutritional Information Disclaimer.