Heat a skillet over medium with enough neutral oil to lightly coat the pan. Fry plantain slices until golden and tender, 3–4 minutes per side. Transfer to a tray and let rest briefly.
Place plantains between parchment and smash until flattened. Return to the skillet with a drizzle of olive oil and fry over medium-high until deeply crisp outside and soft inside. Season with salt.
Toast cardamom, annatto, and saffron in neutral oil until fragrant. Add rice and toast lightly. Pour in beef bone broth, season with salt, cover, and simmer on low for about 15 minutes. Rest 5 minutes, then fluff.
Stir together herbs, shallot, pickled peppers, lemon zest and juice, vinegar, olive oil, salt, and pepper. Adjust to taste.
Spoon rice into bowls and top with crispy smashed plantains, protein if using, and chimichurri. The plantains also work on their own as bite-size tostones.