Mass production of eggs would be the easiest, but staying as realistic as possible, I would provide the following:
The biggest drawback of humans vs most other creatures is our growth rate. There are unconfirmed theories that shows that while growing up, our brains consumes most of the energy our bodies receive, and leaves the body behind. Given this factor, if glucose can be administered biologically through the mother of children to assist in both growth rate of the brain and body we would be able to improve our overall growth rate.
There is a rare condition called macrosomia. This is caused by genetic disorders such as obesity and diabetes. Macrosomia causes babies in the womb too grow at a faster rate and at normal pregnancy times are a lot larger than normal babies. If a mother can be genetically modified to boost this condition along with the high concentration of glucose, it could be possible to have babies born as early as 3 months at the normal size of a 9 month birth.
Twin births are caused when 2 eggs are present in the womb. Given the above factors as well as twin births it would result in a single mother should be capable of producing 6 babies in 9 months and possibly more if the eggs are increased in the womb to create triplets.
At a steady increased growth rate, Children can possibly reach full adulthood at 5 to 6 years of age, a lot sooner if the rate is massive.
There are however other factors to consider. One being overpopulation. Salmon produces hundreds of thousands eggs. If these fish had the lifetime of a human being, it would mean that the population would increase so fast that they would fill the oceans. Food would no longer be readily available and there would be a mass extinction. Instead, they have a life cycle of 3 to 8 years where after spawning, the parents would die. given the rate at which human population would reproduce, the life cycle should be dramatically reduced in order to ensure huge over population does not occur. We would expect a life cycle of a maximum of 20 years, perhaps even less.
Food production would need to increase, this would mean that plant proteins would be the most common as it can be grown quicker than most meat producing animals.
Last, but not least, gender factors of human babies born would need to have a steady ratio. If too little females are born, there would be a very high possibility of in breeding as there are not enough females to go around. If there is too many females, the growth rate of the army would be inefficient.
Given the above ratios of human baby births as twins as well as the fact that all children would be able to produce more children at the age of roughly 6 years old. a single mother should be able to produce around 112 babies in her lifetime. a million mothers would be able to then produce around 112 Million babies in 14 years.
There are rare cases of a mother producing octuplets which if developed instead of twins, could increase this number dramatically.