1. Prepare frozen artichoke hearts as label directs; drain. Cut each artichoke heart length wise in half; set aside.
2. In 3-quart saucepan over high heat, heat water, lemon juice, salt, and chicken bouillon to boiling. Reduce heat to medium-low to maintain simmer.
3. Meanwhile, in 5-quart Dutch oven or sauce-pot over medium heat, in 4 tablespoons hot butter or margarine (1/2 stick), cook onion until tender, stirring occasionally. Add rice; cook, stirring frequently, until rice grains are opaque.
4. Add 2 cups simmering bouillon mixture to rice, stirring until liquid is absorbed. Continue cooking, adding remaining bouillon mixture, 1/2 cup at a time, and stirring after each addition until all liquid is absorbed and rice is tender but still firm, about 30 minutes.
5. Into rice, stir artichoke hearts, peas, mozzarella, Parmesan, and 4 tablespoons butter or margarine (1/2 stick); cook, stirring frequently, until vegetables are heated through and cheese melts.