Preheat a grill. Place the quinoa, 1 3/4 cups of the water and 1/2 teaspoon of the sea salt in a pot over medium-high heat. Bring to a boil. Cover, lower the heat to low, and cook until all liquid is absorbed, about 15 minutes. Remove from heat. Allow to sit for 10 minutes.
Meanwhile, place the remaining 1/4 cup water, 2 tablespoons of the lemon juice, the olive oil, if using, oregano, and thyme, the remaining 1/4 teaspoon of salt, and the black pepper in a shallow baking dish and whisk well. Add the portobello, red bell pepper, hearts of palm, and artichoke hearts and coat well.
Grill the marinated vegetables until tender and char marks appear, 3 to 5 minutes on each side, depending upon the heat of the grill. Chop into 1/2-inch pieces, and place in a large bowl.
Add the cooked quinoa and all the remaining ingredients, including the remaining teaspoon of lemon juice, and gently mix well. Serve warm or cold.