Pat the salmon dry with paper towels and season all over with salt, pepper, paprika, and cumin. Set aside while you prep the veggies.
Heat a large skillet over medium heat. Add one tablespoon of olive oil and swirl to coat.
Add the diced sweet potatoes. Sauté for about 6–8 minutes, stirring occasionally, until they start to soften and brown in spots.
Push the potatoes to one side of the pan. Add the remaining tablespoon of olive oil to the bare side, then lay the seasoned salmon skin-side down (if skin-on) in the oil. Cook for 3–4 minutes until the edges look opaque about a third of the way up the fillet.
Flip the salmon carefully and cook for another 2–3 minutes, just until it flakes easily with a fork. Move the salmon to a plate and tent loosely with foil.
In the same pan, add the minced garlic, stirring for about 30 seconds until fragrant. Add the kale and toss with the potatoes and garlic, letting the greens wilt. If needed, splash in a little water to help steam the kale.
Pour over the lemon juice, season with salt and pepper, and continue to cook for 2–3 minutes until the kale is tender but still bright green.
Return the salmon to the pan to warm through for a minute or so, or serve it on top of the bed of sweet potatoes and kale. Finish with a final squeeze of lemon and a small pat of butter on top for gloss and extra richness.