Nearly every product offered by MEXEM has NO minimum order size. You can place trades with an order size as low as 1 share, 1 contract, 1 unit of currency, etc. Forex order quantity is by default in defined in terms of units of the first currency of the pair. The concept of Forex lots does not apply at MEXEM.
Bond order minimums may vary. When you place an order the Order Ticket or order line should default to the minimum order size, which is also visible in the Order Preview.
See also: How can I search for Bonds?
Mutual Fund orders have an initial fund order minimum of USD 3,000. Subsequent order sizes vary by fund. See the individual prospectuses for more details.