Place a large rimmed baking sheet (or 2 smaller baking sheets) in the oven. Pre-heat the oven to 400 degrees.
Meanwhile, combine the salt, paprika, cinnamon, and pepper in a small bowl.
Place the sweet potatoes and cauliflower in a large mixing bowl. Drizzle with 2½ tablespoons of olive oil and sprinkle with half of the spice mixture. Toss to combine.
Pat the chicken thighs dry with paper towel. Rub the thighs all over with the remaining tablespoon of olive oil and season with the remaining spice mixture.
Place the thighs skin side down on the pre-heated baking sheet(s). Arrange the sweet potatoes and cauliflower around the chicken (not on top of it!) in an even layer, leaving a little space between the vegetables if possible.
Roast the chicken and vegetables for 15 minutes. Remove the baking sheet(s) from the oven. Turn the chicken thighs over and give the vegetables a quick stir. Return to the oven and roast for 15 minutes more (30 minutes total) until the chicken is cooked through and the vegetables are tender and lightly browned. (If you like particularly crispy skin on your chicken and a little char on your veggies, place the sheet pan under the broiler for 1-2 minutes until the chicken skin is browned and super crispy.)
If you used two sheet pans to cook the chicken and veggies, transfer everything to one of the pans or a serving platter. Top with the jalapeño, pomegranate arils, cilantro, and feta. Squeeze the lemon juice over everything and serve warm.