DOUGH: In a small cup or bowl, stir yeast into water. Allow to rest for 5-10 minutes (it should get thick and begin to bubble). Pour into the bowl of a stand mixer fitted with a paddle attachment. Add the milk, beaten egg, pumpkin, melted butter, 1 1/4 c. flour, brown sugar, granulated sugar, salt, cinnamon and pumpkin pie spice. Beat vigorously for 2 minutes.
Attach dough hook to mixer. Slowly add the rest of the flour, a 1/2 cup a time, beat until the dough is stiff and begins to pull away from the bowl.
Turn the dough onto a floured surface. Knead, adding flour if necessary, until the dough is smooth and elastic. Place dough into a greased bowl, turn the dough to coat the entire ball. Cover with plastic wrap and a tea towel, allow to rise in a warm place until doubled in size (approximately 1 hour). If the dough is has not doubled by then, allow it to rise for an additional half hour.
FILLING: Using a fork, combine all of the ingredients in small bowl. Set aside.
Transfer the risen dough to a floured surface and roll into a 16 x 12-inch rectangle. Spread the filling over the dough. Roll into log and cut into 16 1-inch slices using a sharp knife. Place the slices into a greased 9 x 13 baking dish. Cover with a towel and let rise until almost doubled, about 45 minutes.
Preheat oven to 375 degrees. Bake the for 20-25 minutes or until rolls are golden brown.
FROSTING: While rolls are baking, prepare frosting by beating the cream cheese, butter, vanilla, lemon juice and salt in a medium mixing bowl until smooth. Add the confectioners' sugar 1/2 cup at a time. If the mixture becomes too thick, slowly add milk one half tablespoon at a time.
Remove rolls from oven and let cool on wire rack. Frost 5-10 minutes after removal.