Chew your food more thoroughly -- that'll help you digest better and slow you down.
Something that helped my aunt is after every bite put your fork down and ask you self am I still hungry or am I just eating bc it taste good. Sometime she would take two or three bites and realize she wasn't hungry.
You could also try taking a gulp of water with every bite. Then you fill up on more water, your brain will signal that stomach is full from water instead of food.