Preheat a cast iron skillet over medium heat until very very hot.
Peel and chop onion and peel and crush garlic.
Wash and dice tomatoes.
Wash and dry cilantro, destalk and chop.
Add a splash of olive oil to hot skillet, then add shrimp, season with salt and pepper and cook until bright red (depending on the type and size of shrimp you are using this will take between 1 and 3 minutes per side).
Remove cooked shrimp from pan.
Add another splash of olive oil and sauté onion and garlic until onion is translucent.
Add tomatoes and cilantro to skillet, pour in chicken stock, season with salt and pepper and reduce heat to medium-low.
Let simmer uncovered for about 20 minutes.
Peel avocado and cut into slices.
minutes before tomato sauce is done add Capellini pasta to water and stir with a fork every minute or so to ensure they don't stick together.
Once pasta is cooked, drain, quickly rinse with cold water (this is to prevent pasta from sticking together) and then serve in bowls.
Add shrimp to bubbling tomato sauce for about 30 seconds to reheat, then serve over pasta.
Add sliced avocado on the side and sprinkle queso fresco and some fresh cilantro over everything.