Place cod filets in a medium bowl and squeeze lemon juice over them. Set aside.
In a large pot, heat olive oil over medium-high heat. Add thinly sliced onion, red bell pepper, tomato paste, paprika, cumin, and dried oregano. Cook while stirring for 1 minute until vegetables are slightly softened.
Pour in seafood stock and add drained diced tomatoes. Bring mixture to a light boil.
Add white beans, chopped carrots, potatoes, and fresh thyme to the pot. Cover with a lid, reduce the heat to medium-low, and let simmer for about 20 minutes until the vegetables are tender.
Carefully place the cod filets and salt into the pot. Gently stir and break fish apart halfway through cooking until cod is opaque and flakes easily with a fork, about 8 to 10 minutes. Discard thyme sprigs.
Divide the hearty stew among 4 bowls. Serve each bowl with slices of creamy avocado and chopped parsley.